Motor vehicle injury remains a major health problem, accounting for more lost years of pre-retirement life than any other health problem except cancer. Alcohol is a significant factor in serious and fatal motor vehicle injury. While it has long been known that alcohol is associated with injury, the explanation has been that alcohol impairs judgment and psychomotor performance, which it does. However, there is growing evidence that alcohol also increases the amount of injury resulting from an impact of specified dimensions. Limited laboratory research based on animal models shows a linear relationship between amount of alcohol and extent of injury. However, the animal-based studies used acute preparations, that is, one-time administrations of alcohol, quite different from human experience. Previous research by the Principal Investigator, based on human subjects, shows a non-linear relationship,with a higher probability of serious injury occurring at about 0. 10 - 0. 15 BAC and above 0.25 BAC than occurs for the interim BACs. It is hypothesized that the non-linear relationship is attributable to differences in drinking histories and levels of tolerance to alcohol. This project will examine, for the first time, the potentiating effects of alcohol on injury, taking into account history of alcohol use and evidence of tolerance (both behavioral and biomedical). There is growing evidence that illicit drugs are increasingly involved in traumatic injury, but studies thus far have been limited to serious (patients admitted to major trauma centers) and fatal injuries and have not addressed the full spectrum of injury. As with alcohol, it is important to examine the full range of injury to understand the nature and extent of the drug-injury relationship, including its interaction with alcohol and how it differs from alcohol. The aims of this study are to 1) expand the limited clinical investigation of the relationship between alcohol and extent of injury sustained, taking into account other injury-related factors; 2) investigate whether and to what extent the potentiating effects of alcohol on injury vary as a function of drinking history and tolerance; 3) expand limited information on the relationship between illicit drug use (marijuana, cocaine, opiates) and injury to include the full spectrum of injury; and, 4) initiate exploration of any potentiating effects of these drugs on injury. The findings will expand and clarify the clinical information on the potentiating effects of alcohol on injury; determine the relationship between illicit drugs and motor vehicle injury, examining the full range of injury and considering other relevant factors; and determine the relationship between alcohol and the use of illicit drugs in the full spectrum of injury severity, from minor to fatal. The results will have significance for alcohol and drug education, for pre-hospital and hospital care of the injured patient, and for hospital-initiated interventions to provide assistance for alcohol and other drug-related problems.